With a significant increase in the amount of information, there is an eager demand for the realization of a large volume information recording apparatus. In the hard disk drive (HDD) technology, a high recording density is achieved. Thus, various techniques concentrating on perpendicular magnetic recording have been developed. Further, a patterned medium is suggested as a medium which satisfies both the improvement in recording density and the thermal fluctuation resistance. The technique for manufacturing the medium has been actively developed.
The patterned medium records one or more magnetic areas as one cell. In order to record 1-bit information in one cell, it is possible that recording cells are magnetically separated. Therefore, a magnetic dot portion and a nonmagnetic portion may be formed on the same flat surface using a fine processing technology. There is a method for producing a fine concave-convex pattern is formed on a magnetic recording layer formed on a substrate using a semiconductor manufacturing technology. Then, the pattern is physically divided to obtain magnetically independent patterns.
In order to form a magnetic dot pattern, it suffices that a mask is previously formed on a magnetic film and the concave-convex pattern is transferred. Alternatively, there is a method for forming a concave-convex pattern on a mask material and injecting ions irradiated with high energy into a magnetic area so as to allow the pattern to be selectively deactivated, or a method for pressing a concave-convex mold against a resist material so as to transfer the concave-convex pattern.
In order to prevent the abrasion of the surface of the medium caused by magnetic head scanning and prevent the corrosion when being exposed to the outside environment, a protective film is usually formed on the magnetic film having a concave-convex pattern. The protective film needs to be formed into a thin film in order to narrow the magnetic spacing for receiving magnetic field signals from the magnetic recording layer with high efficiency. Also, it is necessary to ensure the thickness for preventing the corrosion.
In the case where the protective film is formed on the convexo-concave portion of the magnetic recording layer formed on the substrate, when the pattern pitch is sufficiently large, the protective film uniformly covers the upper and side surfaces of the pattern. Accordingly, it is possible to prevent the surface smoothness from being impaired. However, in a patterned medium aiming at high recording density, a distance between convexo-concave portions becomes significantly narrow. Thus, the protective film is not uniformly formed and the positional dependence of the roughness difference between the concave-convex portions becomes higher. Consequently, the flying stability of the magnetic head is deteriorated and it impossible to avoid a decrease in an S/N signal. Further, in the case of the coexistence of a data area where a pattern for identifying digital signals “1” and “0” is arranged and a servo area which has the responsibility of the positioning information of the head, the density (sparse or dense) of the pattern is high, and thus the protective film is not uniformly coated. Therefore, the coatability of the protective film in the concave-convex pattern with a narrow pitch is an important measure directly linked to the improvement in the flying stability of the head and the improvement in the S/N signal by the reduction in the magnetic spacing.
For example, in a technique comprising using a concave-convex pattern formed on a substrate as an underlayer and forming a magnetic film to produce a magnetic recording concave-convex pattern, the pattern having a protective film thereon has a big roughness difference between the concave-convex portions. Thus, the flying stability is deteriorated and there is a problem of a decrease in the S/N signal.
For example, in a technique comprising selectively etching a grain boundary portion of a magnetic recording layer formed on a substrate to produce a magnetic recording concave-convex pattern, it has been difficult to solve the same problem as that of Patent Literature 1.